Origin

Mid 17th century (in the sense 'having two modes of existence or of doubtful nature'): from modern Latinamphibium 'an amphibian', from Greekamphibion (noun use of amphibios 'living both in water and on land', from amphi 'both' + bios 'life').

Amphibians live both in water and on land, and it is the idea of ‘living in both’ that gives us the word, which comes from Greek amphi ‘both’ (also found in amphitheatre (Late Middle English) from amphi ‘on both sides’ and theatron ‘place for beholding’) and bios ‘life’, source of words such as biology (early 19th century) and antibiotic (mid 19th century). Before it was applied specifically to frogs, toads, and newts, amphibian simply meant ‘having two modes of existence, of doubtful nature’.